1. Technical Field
The present invention is directed toward fixed cellular terminals, and more particularly toward single line fixed cellular terminals adapted to provide continuous and reliable telephone service.
2. Background Art
Cellular telephone systems are, of course, growing explosively throughout the world. Such systems are widely known to allow telephones using such systems to be mobile, with the telephones taken by the users wherever they go.
Cellular telephone systems are also advantageously used, however, in conventional applications where the phones are fixed. Particularly in locations where there is a growing need for service but the infrastructure is inadequate or nonexistent, it costly and time consuming the lay conventional phone lines so as to reach each home, office or other location where telephone service is desired. As a result, people in such areas wanting such service can be forced to wait months or even years for service. Further, particularly in low density areas, the cost of laying such lines to widely separated locations can be cost ineffective. Cellular telephone systems provide an ideal solution to such problems, as a cellular tower can be installed to establish a cellular network covering a wide area at a much lower cost, and much more quickly, than conventional telephone service with ground lines to each service location.
In such cases, a fixed cellular terminal (FCT) is provided at the location where telephone service is desired. The fixed cellular terminal (which is one embodiment of a wireless local loop [WLL] terminal) is a cellular communications device, installed at the location where service is desired, to which standard (non-cellular) devices such as dual-tone, multiple frequency (DTMF) telephones, telefaxes and/or modems may be connected by their standard 2-wire connection.
A common configuration for installation at such locations is a single line fixed cellular terminal (SLT), which consists of a single line module (SLM) and power supply with battery backup. The single line module includes a line interface controller through which the standard DTMF devices may be connected, with three such devices typically being connectable at the same time using ordinary telephone jacks. (This thus also makes fixed cellular terminals well suited for temporary use until fixed lines can be laid if that is desired, as the building can be internally wired in a conventional manner with ordinary jacks, wires, etc., with such wiring then readily usable with the ground line once laid by connecting into the building system at the location of the line interface controller.) The SLT provides an interface with the cellular network in accordance with whatever standards may be used by that network. Such a configuration is shown in FIG. 1 and described in further detail below.
Unfortunately, despite the significant advantages as described above for fixed cellular terminals, they encounter problems not typically recognized with mobile cellular telephones. That is, mobile cellular telephones are not expected to operate continuously for extended periods of time, since normal operation of a mobile terminal is usually limited by the life of its battery, and most users of such phones frequently turn them on and off in any event. By contrast, as a replacement for standard wireline phones, fixed cellular terminals are typically required to operate continuously, even though typical software for cellular terminals is neither fault tolerant nor does it automatically recover from all error conditions.
As a result of the above, faults or errors which might be incurred during long periods of continuous operation can cause the terminal to xe2x80x9clock-upxe2x80x9d and not process telephone calls. In some such cases, the cellular terminal itself might not know that a problem exists and therefore report incorrectly to the line interface controller that it is operational. This is due to the fact that the software within the terminal is typically implemented in layers, and error detection and fault handling between layers does not identify all error modes. A failure in a lower layer of the software could be undetected by any of the upper layers.
Such problems can have serious consequences. Since the terminal does not recognize that it is not operating properly, it will obviously not take corrective action to correct the problem, nor will it give any indication to the user that he or she should take corrective action. As a result, the terminal may remain inoperable for long periods of time. In a situation where the user does not make many outgoing calls (at which time he or she might discover the error), the user may unknowingly miss many incoming calls. Besides the obvious irritation to customers in being unable to rely on their phone service (imagine a businessperson being away and unable to get through to check messages, perhaps realizing that there are no messages because customers are also unable to get through to your line), lost calls always have the potential for serious adverse consequences, whether they be personal or business.
As a result of this problem, some fixed wireless equipment providers refuse to guarantee continuous operation of their fixed cellular terminals. One solution to the problem has been to turn the cellular terminal off and on at a regular interval (usually many hours apart), as this essentially resets the software to clean up any problems which might have developed in the software, in much the same way that turning a personal computer off and on will reset its software to eliminate problems. However, this reset operation would occur whether or not there is an error condition present and, since the terminal is unable to place or receive calls while resetting, a call which would otherwise get through might be lost. Further, if the error condition arises early in the period between resets, the problems with lost calls and unrecognized inoperability will continue for the long period of time until the next reset. Minimizing the duration of such inoperability by shortening the time between resets would increase the first mentioned problem by proportionately increasing the times when the terminal is unable to place or receive calls.
The present invention is directed toward overcoming one or more of the problems set forth above.
In one aspect of the present invention, an improvement is provided for a cellular terminal adapted to connect a telephone communication device to a cellular telephone network, which terminal includes a transmitter periodically sending a registration signal to the network and a receiver receiving acknowledgement signals sent by the cellular telephone network in response to the registration signals. The improvement includes a counter recording the number of consecutive acknowledgement signals not timely received by the cellular terminal, and means for initiating corrective action to reestablish proper connection between the cellular terminal and the cellular telephone network when the number recorded by the counter exceeds a selected number.
In preferred forms of this aspect of the present invention, corrective action is initiated by signalling an error condition to a user of the cellular terminal and/or by generating an instruction signal causing the cellular terminal to reset.
In another preferred form of this aspect of the present invention, the selected number used to determine when to initiate corrective action may be changed.
In another aspect of the present invention, an improvement is provided to a fixed cellular terminal to continuously connect a non-mobile telephone communication device to a cellular telephone network, where the terminal includes a transmitter periodically sending a registration signal to the network in accordance with instructions received when initially connecting to the network and a receiver receiving acknowledgement signals sent by the network in response to the registration signals. The improvement includes means for recording whether an acknowledgement signal is received at the cellular terminal in response to a sent registration signal, a counter incrementally increased when the recording means records that an acknowledgement signal was not received, the counter being reset to zero when the recording means records that an acknowledgement signal is received, and means for initiating corrective action to reestablish proper connection between the cellular terminal and the cellular telephone network when the counter exceeds a threshold.
In a preferred form of this aspect of the present invention, the threshold may be configured in accordance with the environment within which the terminal is located.
In other preferred forms of this aspect of the present invention, corrective action is initiated by signalling an error condition to a user of the fixed cellular terminal and/or by generating an instruction signal causing the cellular terminal to reset.
Another aspect of the present invention is a method of providing continuous verified interaction of a cellular terminal with a cellular telephone network, comprising the steps of (1) sending periodic registration messages from the cellular terminal to the cellular telephone network, (2) sending acknowledgement signals from the network to the terminal in response to registration messages, (3) counting the number of consecutive acknowledgement signals not timely received by the cellular terminal, and (4) initiating correction of a failure of interaction of the cellular terminal and the cellular telephone network when the counted number of consecutive acknowledgement signals not timely received reaches a selected number.
In a preferred form of this aspect of the invention, the time interval between periodic registration messages is fixed in response to instructions received from the cellular network when first establishing interaction between the cellular terminal and the cellular telephone network.
In other preferred forms of this aspect of the invention, the initiating step sends a signal to the user indicating a failure of interaction of the cellular terminal and the cellular telephone network, and/or resets the cellular terminal.
It is an object of the present invention to provide a cellular telephone terminal which can be relied upon to provide substantially continuous service for indefinite extended periods of time.